Contact member for electric clocks and watches



y 7, 1964 i w. TlLSE ETAL 3,140,376

CONTACT MEMBER FOR ELECTRIC CLOCKS AND WATCHES Filed Dec. 28, 1960 3Sheets-Shee t 1 I 1| [I ll 9 l I l I JIWENTOES. WIL HELM TILSE JOSEFEGGER A TTORNEYS.

July 7, 1964 w, TlLSE ETAL 3,140,376

CONTACT MEMBER FOR ELECTRIC CLOCKS AND WATCHES Filed Dec. 28, 1960 3Sheets-Sheet 2 A T TOR rs July 7, 1964 1 w. TILSE ETAL 3,140,376

CONTACT MEMBER FOR ELECTRIC CLOCKS AND WATCHES Filed Dec. 28, 1960 sSheets-Sheet :5

FIG.7 FIGS IZFTGII FIG.I2

lwmrms.

W/L HELM T/LSE JOSEF EGGER.

United States Patent 3,140,376 CONTACT MEMBER FOR ELECTRIC CLOCKS ANDWATCHES Wilhelm Tilse, Pforzheim-Birkenfeld, and Josef Egger, Pforzheim,Germany, assignors to The United States Time Corporation, Waterbury,Conn., a corporation of Connecticut Filed Dec. 28, 1960, Ser. No. 78,964Claims priority, application Germany Jan. 9, 1960 2 Claims. (Cl. 200166)This invention relates to electric clocks and watches of the type havingan oscillating balance wheel or pendulum powered by the reaction betweena steady magnetic field and a pulsating magnetic field. In particular,the invention relates to improvements in electrical switches forgenerating the magnetic impulses in mechanisms of this type where theswitch is periodically closed by the rotating member at fixed points ineach cycle of oscillation.

Devices of this type are generally divided into two classes, the firstcomprising a plurality of fixed permanent magnets and a moving coil, thesecond comprising a fixed coil and moving permanent magnets disposed onthe oscillating member. Both classes use a mechanically activatedelectrical switch member intermittently to connect a source of directcurrent to the coil to provide a pulsed magnetic field which reacts withthe permanent magnetic field to push the oscillating rotary membereither once or twice .during each cycle of oscillation. The currentsource thus supplies energy to the system to overcome frictional lossesand to power the gear train which drives the hands of the watch.

One of the principal disadvantages of systems in current use has residedin the mechanical switch, which is necessarily subjected to millions ofclosures in normal usage, the consequent wear resulting in a decrease ofdependability with age. Aside from the normal wear resulting fromfriction, there occurs physical deterioration of the contacts resultingfrom the inherent sparking which occurs during the making and breakingof the electrical circuit. Where, as in the usual case, one of thecontact members is spring mounted, and thereby subject to vibrationalmovements, the problem is magnified, because on each primary closing ofthe contacts the spring-mounted contact is subjected to naturaltransverse oscillations induced by the shock of the main impact. Thisresults in bounce or chatter of the contacts which occurs prior tomaking complete connection. This bouncing or chattering increases theerosion of the contacts resulting from the numerous spark discharges,causing a proportionate decrease in contact life.

My present invention is directed to methods and apparatus for minimizingcontact bounce and sparking between contacts in order to extend theuseful life of contact members.

A feature of my invention is the addition of a loosely coupled dampingweight disposed on the vibrating contact member to dampen the vibrationswhich occur first when the contacts close and second when the contactsbreak as the moving contact member swings beyond and free from the fixedcontact member. Damping of this secondary vibration which occurs onseparation is necessary to insure :that the spring contact member hassubstantially ceased vibrating by the time the second impact takesplace.

Another feature of my invention resides in a novel arrangement of theoscillating contact member. To further guard against contact bounce andchatter on the closing impact, I arrange an insulating member either onthe contact spring or on the moving contact in such a manner that thefirst physical connection takes place between one contact and theinsulating member. With this arrangement no electrical contact, andconsequently no sparking,

3,140,376 Patented July 7, 1964 occurs until all vibrations areeffectively terminated. Thereafter, sliding electrical contact is madegiving a wiping action between the contacts that promotes selfcleaning.

A further feature of the invention involves the shaping of thestationary spring contact area to minimize the electrical contact areato a virtual point contact and to promote wiping action of the contacts.

These and other features of the invention will be better understood byreference to the accompanying drawings, showing a preferred embodiment,in which:

FIG. 1 is an elevation view, partly in section, of an electric watch,embodying the invention along line 11 of FIG. 2;

FIG. 2 is a plan view of the principal elements of theelectro-mechanical portion of the watch of FIG. 1 as viewed along line22 of FIG. 1;

FIGS. 3 to 6 illustrate the switching action, step-by-step, during onesweep of the balance wheel;

FIGS. 7 to 10 illustrate various forms of the damped spring contactmember; and

FIGS. 11 to 13 are sectional views of the preferred type of contactmember as illustrated in FIGS. 7 to 10.

The main elements of an electric watch embodying the present inventionare shown in elevation and partly in section in FIG. 1, the sectionbeing taken along line 11 of FIG. 2. A balance wheel body 20 ofnon-magnetic material is arranged on a balance staff 14 which isjournaled at its upper end in the balance cock 10 and at its lower endin the pillar plate 11. Also included on the staff 14 are thehair-spring 16, secured to the collet 18 at its inner end and to thestud 17 at its outer end in the usual manner, and upper and lower rollertables 30 and 35, respectively. The lower roller table 35 has aneccentric roller jewel 37 adapted to engage and drive the gear train,generally indicated at 38, in the normal arrangement. The upper rollertable 30 has a flanged portion 31 supporting a crescent-shaped pin 32which may be a jewel or other non-conducting material.

The balance wheel body 20 carries a sector-shaped coil 25 which isadapted to react magnetically to a series of three alternately polarizedpermanent magnets 40 which are disposed on the pillar plate 11. Themagnetic axes of the magnets are parallel to the axis of the balancestaif 14. One end 28 of the coil 25 is electrically connected to thebalance wheel which is grounded to the pillar plate via hair-spring 16and stud 17. The other end 27 of the coil 25 is electrically connectedto a cylindrical contact pin 26 aligned along a radius of the balancestaff directly outside the upper roller jewel 32. The pin 26 is mountedon but insulated electrically from the balance wheel body 20 by theinsulated insert 24.

An electrical contact member, generally indicated at 43, includes anelongated spring member 44, mounted at its extremity in an insulatedblock or base 49 secured in any suitable manner to the pillar plate 11,as by stud 41. The contact member 43 is electrically connected via wire51 to a source of voltage 50 which may be a small dry cell enclosedeither internally within the movement or externally in the watch band,not illustrated. The other electrode of the battery 50 is suitablyconnected to the ground circuit which includes the pillar plate 11 andthe watchcase itself, not shown. The electrical contact member 43 asshown in FIG. 2, includes a spring finger 44 having at its otherextremity a contact area 45 which is adapted periodically to contact thepin 26 twice during each cycle of oscillation of the balance wheel 20.

One of the features of this invention resides in the physicalarrangement of the spring contact member 43, and a preferred embodimentthereof is illustrated in FIGS. 1 through 6 inclusive. Other suitableforms of the spring contact member, to be hereinafter described, areillustrated in FIGS. 7 to 10 inclusive.

FIG. 2 illustrates the preferred form of spring contact member 43. Thespring 43 is preferably of hairpin shape, having a longer leg 44 and ashorter leg 46 interconnected by the curved contact portion 45. Themember is mounted in such a manner that the center of the radius ofcurvature of the portion 45 lies along a line which intersects the axisof staff 14. A damping member 48 is disposed on the leg 44 at a point tobe hereinafter described. The shorter leg 46 is bent at its outerextremity into the form of an inwardly projecting V so that the apex ofthe V lies close to the inside edge of the leg 4-4. The ringshapeddamping member 48 is arranged to loop loosely the two legs 44 and 46 attheir closest point. The weight of the damper 48 is selected so that itsnatural resonant frequency of vibration in a transverse directiondiffers from the natural resonant frequency of transverse vibration ofthe spring member 43, thus serving to damp vibrations of the springmember resulting from the impact of the oscillating balance wheelassembly. It is to be noted that the damper 48 is free to vibratetransversely to the longitudinal axis of the spring member 48 but isrestricted from longitudinal movement along the leg 44.

It is advantageous to select the longitudinal location of the dampermember 48 on the basis of the following criteria. It is well-known thattransverse vibrations of a bar clamped at one end include a fundamentalresonant frequency of vibration which may be calculated from knownformulae, as, for instance, those illustrated and discussed in the bookby Harry F. Olson entitled Elements of Acoustical Engineering, publishedin 1940 by the D. Van Nostrand Company, Inc., in Section 3.3 at pages 38and 39. As also pointed out by Olson, harmonic vibrations or overtonesalso are present in the vibrating bar. These secondary vibrations haveantinodes, or points of maximum deflection, existing at discrete pointsalong the bar. For example, the first overtone has an antinode locatedapproximately halfway along the bar while the second overtone has anantinode located approximately two-thirds the way along the length ofthe bar, as measured from the fixed end. It has been found thatsurprisingly effective damping occurs if the damper member 48 is locatedat any point within the region between onehalf and two-thirds of thelength of the member as measured from the fixed end.

Systems subjected to vibrational oscillation as a result of someinitially applied force are known to have specific vibration decaycharacteristics dependent on such factors as length, density, modulus ofelasticity and radius of gyration of the body. For example, a certainspring member may have a vibration decay characteristic of one-tenth ofa second. This represents the length of time, as measured from theinitial application of energy, to the point when for all practicalpurposes the vibrations have ceased. When a damping weight is attachedto the body in the proper manner it is possible to shorten the vibrationdecay characteristic from one-tenth of a second to, say, one-twentiethof a second or less. The weight of the damping member may be increased,however, further to shorten the decay characteristic to, say,one-fortieth of a second if desired. A further factor must be consideredin determining the weight of the damping memher, that is, if the Weightis too heavy, the impedance which the weighted spring contact memberpresents to the rotating balance wheel during each sweep of the balancemay disturb the natural period of oscillation sufficiently to cause itto lose its inherent isochronous properties essential to its accuratetimekeeping function. Thus the Weight as well as the position of thedamping member 48 must be selected from optimum performance.

A still further factor to be considered in obtaining optimum performanceof the spring and damper assembly is the physical size of the dampingmember. By that is meant primarily the size of the internal opening withrespect to the dimensions of the spring. The actions of these twocombined members may not be analyzed by simple harmonic motion theorysince the damping weight is only loosely interconnected with the springmember. The damping ring is essentially free to move transversely inspace but limited in the vertical and longitudinal directions. The ringonce set in transverse motion in a given direction continues moving inthat direction until it strikes the spring or is struck by the springand moved in a different direction. It has been found that the optimumsize and weight of the damping member are achieved when the contactspring and the damping member strike each other after the contact springhas undergone one complete cycle of oscillation (from zero to maximumdeflection in the direction of movement of the contact pin, to zero, tomaximum deflection in the opposite direction, and back to zero) and isabout to commence its second oscillation, and after the damping ring hascompleted only one half an oscillation (from zero to maximum deflectionand back to zero) and is passing through zero in the opposite direction.It has been determined that the optimum sized damping weight willundergo deflections of substantially one-half the deflection of thecontact spring measured at the point of contact.

For a preferred embodiment of the invention it has been determined, in asystem of the type illustrated in FIGS. 1 through 6 having a balance 20weighing 0.3 gram and having a periodicity, in combination with thehairspring, of 6 beats per second, that a contact spring 44 of preciousmetal having a cross-sectional dimension of 0.2 millimeter by 0.04millimeter, an overall length of 9.0 millimeters and weight of 1.3micrograms; a damping member of toroidal shape having an internaldiameter of .32 millimeter and an external diameter of 0.6 millimeter,weighing 1.0 microgram positioned 5.5 millimeters from the fixed endthereof provides satisfactory operation.

Other suitable forms of the spring contact member 43 are illustrated inFIGS. 7 through 10 inclusive, where the spring member is a straight rodor bar fixed at one end. In FIG. 7 the damper 63 comprises an L-shapedmember, having an outer ring part 65, and an inner ring part 64 coupledto a ring 62 disposed in the holding member 61. FIG. 8 illustrates aform of spring 70 having a one-turn loop '71 which interlinks theannular damper weight '72. FIG. 9 shows a further form wherein thehailpin-shaped spring is inverted with the shorter leg having a loop 76at its extremity interconnecting the annular damper 77. FIG. 10 depictsa further variation in form wherein a straight spring member 80 has atransverse slotted opening therethrough to receive a freely slidingmember 81. The member 81 has weights 82 and 83 at its extremities whichprovide the damping action and prevent separation of the members.

Another feature of my invention resides in the shaping of the end of thespring member to provide for eflicient and long-wearing electricalconnection between it and the pin 26. The active contact area 45 of thespring contact 43 may be curved. This promotes removal of oxidationproducts from the contact surfaces that form as a result of thesparking. However, the most desirable arrangement results if the end ofthe spring finger has a spherical shape in its contact area. With thepreferred form of contact spring, as shown in FIGS. 1 to 6, the arcuateportion 45 may be ground or formed as illustrated in FIGS. 11 through13. FIG. 11 is an enlarged plan view of the end of the spring member 85.FIG. 12 illustrates the cross-sectional shape of the member taken alongline 121l2 of FIG. 11. FIG. 13 illustrates the cross-sectional shape ofthe arcuate portion 87 as taken along line 1313 of FIG. 11. When the endof the fixed contact member is spherical, as depicted, only line contactis established between the contacts during a sweep of the balance wheel,and at any particular instant of time during the contact period onlyvirtual point contact exists between the bodies. The wiping action whichis inherent serves to clean the surface of the contact areas of anyoxidation products produced by sparking.

A further feature of my invention resides in the arrangement of therotating contact pin 26 and the insulated member 32. In describing thefunction of the insulating member 32, reference is made to FIGS. 3 to 6inclusive, which illustrate the various positions assumed by the twoelectrical contacts during one counterclockwise sweep of the balancewheel. In FIG. 3, the spring finger 43 is in its neutral or at-restposition and the balance wheel is turning counterclockwise, as indicatedby the arrow P. As seen in FIG. 4, the first impact between the two metbers occurs between the arcuate portion 45 of the spring member 43 andan edge of the insulating pin 32. At this position, the member 43undergoes vibrating oscillations as a result of the impact, and anyresidual contact bounce which has not been completely eliminated by thedamper 48 will rapidly subside or decay prior to the first electricalcontact and therefore without the usual numerous spark discharges,energy loss and pitting. As seen in FIG. 5, after the vibration ofspring contact 43 has dissipated, the further counter-rotation of thebalance wheel causes electrical connection to be established graduallybetween member 43 and pin 26. FIG. 6 depicts further counter-rotation ofthe balance wheel to the point where the member 43 is about to slide ofithe pin 26 and break the electrical circuit. Member 43 now being undertension snaps away from the pin 26 to minimize the spark dischargeresulting from the collapse of the magnetic field in coil 25. At thispoint, member 43 again enters upon a vibratory state which is quicklyarrested by the action of damper 48 prior to the subsequent impact bythe opposite edge of insulating pin or bumper 32, during the reversehalf-cycle of oscillation of the balance wheel.

While each of the features described above including the addition of adamping weight to the spring, the shaping of the contacts to provideonly point contact at any instant and use of an insulated bumper toprovide initial physical connection and vibration absorption prior toelectrical connection of the contacts in themselves, tend to reducesparking, combinations of any two of the features will yield furtherreduction in sparking. In the preferred embodiment of the invention Iinclude all three features simultaneously to virtually eliminate allsparking problems.

What is claimed is:

1. A fixed electrical switch contact member adapted to cooperate with arotating switch contact member comprising an elongated member of springmaterial supported at one end thereof at a point remote from therotating contact member, the other end of said spring member beingadapted to contact periodically said rotating contact member, saidspring member having a damping member thereon disposed at a pointintermediate the ends thereof, wherein the switch member is of hairpinshape and has two leg portions and an arcuate portion interconnectingsaid leg portions, one of said legs is longer than the other and adaptedfor mounting said member at its extremity, the shorter of said legs hasan inward V-shaped bend near its extremity, and said damping member isringshaped and disposed to link loosely both legs at the notch of the Vbend.

2. A fixed electrical switch contact member adapted to cooperate with arotating switch contact member comprising an elongated member of springmaterial supported at one end thereof on a base at a point remote fromthe rotating contact member, the other end of said spring member beingadapted to contact periodically said rotating contact member, saidspring member having a damping member thereon disposed at a pointintermediate the ends thereof, wherein the switch member is of hairpinshape and has two legs and an arcuate portion interconnecting said legs,one of said legs is longer than the other and adapted for mounting saidmember at the legs extremity, means on a leg portion of the switchmember holds the damping member against longitudinal movement along saidswitch member and permits movement transverse to the axis of the springmember, and said damping member is ring-shaped, loosely surrounds a legof the switch member, and is unconnected to the base and the legs.

References Cited in the file of this patent UNITED STATES PATENTS2,088,411 Fagley July 27, 1937 2,494,622 Lamb Jan. 17, 1950 2,599,953Summers June 10, 1952 2,847,529 Munn Aug. 12, 1958 2,874,251 DreyfusFeb. 17, 1959 2,887,551 Detwiler May 19, 1959 FOREIGN PATENTS 161,786Australia Aug. 27, 1953 1,001,719 Germany Jan. 31, 1957 1,037,676 FranceJune 9, 1958

1. A FIXED ELECTRICAL SWITCH CONTACT MEMBER ADAPTED TO COOPERATE WITH AROTATING SWITCH CONTACT MEMBER COMPRISING AN ELONGATED MEMBER OF SPRINGMATERIAL SUPPORTED AT ONE END THEREOF AT A POINT REMOTE FROM THEROTATING CONTACT MEMBER, THE OTHER END OF SAID SPRING MEMBER BEINGADAPTED TO CONTACT PERIODICALLY SAID ROTATING CONTACT MEMBER, SAIDSPRING MEMBER HAVING A DAMPING MEMBER THEREON DISPOSED AT A POINTINTERMEDIATE THE ENDS THEREOF, WHEREIN THE SWITCH MEMBER IS OF HAIRPINSHAPE AND HAS TWO LEG PORTIONS AND AN ARCUATE PORTION INTERCONNECTINGSAID LEG PORTIONS, ONE OF SAID LEGS IS LONGER THAN THE OTHER AND ADAPTEDFOR MOUNTING SAID MEMBER AT ITS EXTREMITY, THE SHORTER OF SAID LEGS HASAN INWARD V-SHAPED BEND NEAR ITS EXTREMITY, AND SAID DAMPING MEMBER ISRINGSHAPED AND DISPOSED TO LINK LOOSELY BOTH LEGS AT THE NOTCH OF THE VBEND.